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Are Your Allergy Meds Hurting Your Muscle Growth?

New research says antihistamines could block certain genes that impact muscle recovery post-workout.

If you suffer from allergies, you're probably very familiar with the symptoms: itching, sneezing, running nose, and watery eyes. They're triggered thanks to allergens like animal dander, pollen, and mold in the air that mess with your body's "histamine receptors," according to the Mayo Clinic. That's where antihistamines, like Benadryl, Clarinex, and Zyrtec, come in to play—to prevent allergy symptoms by relieving the effects.

Now that we're in the thick of spring allergy season, antihistamines are important now more than ever. But new research from the University of Oregon suggests antihistamines may be affecting our ability to recover from exercise—and it's not a change for the good.

After a grueling workout session, some 3,000 genes in your body go to work to aid recovery by relaxing blood vessels, amping blood flow, and boosting your muscles; but researchers believe high doses of antihistamines can blunt these gene responses and hurt your recovery and muscle gains in the process. Back in 2005, U. of Oregon researcher John R. Halliwill found when certain histamine receptors are over-activated, they drop blood pressure. 

In this study, a new team of researchers had 16 physically fit and active men (10) and women (6), ranging in age from 23-25, perform an hour of knee-extension exercises at 60 percent of their peak power. Half of the participants took 540mg of fexofenadine (an antihistamine in brand name medications Mucinex and Allegra that treats hay fever symptoms) and 300mg of ranitidine (a stomach medicine in the brand name medication Zantac that has some antihistamine effect)—it's important to note that these are levels that expand nearly three times the recommended dosages of over-the-counter antihistamines. 

During exercise, blood flow, blood pressure, and heart rate were monitored. And, researchers conducted muscle biopsies on participants' quads and thighs before and three hours after exercise. This three-hour recovery window allowed the researchers to study genes involved in recovery responses beyond previous research that found histamine improved blood flow for two hours after exercise.

Ultimately, the antihistamines had no effect prior to exercise and little influence on gene expression at the end of the workout. But, three hours after exercise, 88 percent of the 795 genes affected by the antihistamines mostly responded with lower levels of expression. Think of it like a blocked cell phone signal. If your communication is being disrupted, you can't get your message across as effectively. In short, these genes weren't able to function at their highest level and aid in muscle recovery. 

The bottom line:
Should you avoid taking antihistamines when you exercise? Don't ditch them just yet, lead study author Steven Romero said in a press release.

"We need to do a training study in which we put people on histamine blockers and see if their adaptations to exercise training are as robust or diminished," Romero said. "I also wouldn't be surprised if we can demonstrate that some responses to exercise training do become blunted if you take high doses of histamine blockers."

What you can do is stick to the normal dosage recommended on the packaging. 

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